1. Field of the Invention
The present invention generally relates to a wheel support bearing assembly for use in the field of automotive vehicles and, more particularly, to the sealing structure in the wheel support bearing assembly.
2. Description of the Related Art
In general, wheel support bearing assemblies used in, for example, automotive vehicles are used or operated under harsh environments as they are often exposed to rugged and/or wet road surfaces. Therefore, the wheel support bearing assemblies are required to have a relatively high effect of avoiding an undesirable intrusion of dust and muddy water from outside of an automotive vehicle and, also, a relatively high capability of avoiding an undesirable leakage of a grease used as a lubricant.
In view of the foregoing, such a sealing structure as shown in FIGS. 12 and 13A and 13B, for example, has been employed. The wheel support bearing assembly utilizing the sealing structure shown in FIGS. 12 and 13A and 13B includes a generally cylindrical inner member 32, a generally cylindrical outer member 31 positioned radially outwardly of the inner member 32 with an annular working space or a bearing space defined between it and the inner member 32, and a plurality of, for example, two, circumferentially extending rows of rolling elements 33 operatively accommodated within the annular working space and rollingly engaged in part in inner raceways 35 defined in an outer peripheral surface of the inner member 32 and in part in outer raceways 34 defined in an inner peripheral surface of the outer member 31. The annular working space delimited between the inner and outer members 32 and 31 has its opposite, outboard and inboard open ends sealed respectively by outboard and inboard sealing members 37 and 38 each having one or more elastic sealing lips.
An outboard portion of the wheel support bearing assembly, which is encompassed by the circle E in FIG. 12, is shown in FIG. 13A on an enlarged scale. The outboard sealing member 37 is of a structure including an elastic member 40 fitted to a core meal 39. This elastic member 40 is made up of three elastic sealing lips 40a, 40b and 40c slidably engageable with a seal contact surface 32c defined in an outboard portion of the outer peripheral surface of the inner member 32. Of those elastic sealing lips, the elastic sealing lip 40a is utilized to prevent a grease, filled in the annular working space, from leaking and is so tailored as to extend generally axially inwardly of the annular working space in a direction towards the inboard side. The remaining elastic sealing lips 40b and 40c are utilized to avoid an undesirable ingress of dust and muddy water from outside of the annular working space.
Similarly, an inboard portion of the wheel support bearing assembly, which is encompassed by the circle F in FIG. 12, is shown in FIG. 13B on an enlarged scale. The inboard sealing member 38 is of a structure including an elastic member 42 fitted to a core metal 41. The elastic member 42 has three elastic sealing lips 42a, 42b and 42c slidingly engageable with a seal contact member 45 fixedly mounted on the outer peripheral surface of the inner member 32. Of those elastic sealing lips, the elastic sealing lip 42a is utilized to prevent the grease, filled in the annular working space, from leaking and is so tailored as to extend generally axially inwardly of the annular working. The remaining elastic sealing lips 42b and 42c are utilized to avoid an undesirable ingress of dust and muddy water from outside of the annular working space. It is to be noted that the seal contact member 45 referred to above serves as a slinger.
The wheel support bearing assembly utilizing the sealing structure shown in and described with reference to FIGS. 12 and 13A and 13B makes use of the outer board and inboard sealing members 37 and 38 each including the slidably contacting elastic sealing lips 40a to 40c and 42a to 42c. Accordingly, the sealing structure is effective to provide a satisfactory sealing performance.
Since however, the outboard and inboard sealing members 37 and 38 are a contact seal in which the elastic sealing lips 40a to 40c and 42a to 42c slidingly contact the outboard portion of the outer peripheral surface of the inner member 32 and the seal contact member 45, respectively, a high frictional resistance is involved in the seal contact regions. Also, the sealing members 37 and 38 tend to cause a phenomenon that when air confined within the annular working space expands thermally as a result of generation of heat during the operation of the wheel support bearing assembly, that is, during rotation of one of the outer and inner members 31 and 32 relative to the other of the outer and inner members 31 and 32, the elastic sealing lips 40a and 42a that are positioned axially inwardly of the annular working space are forced to contact the respective sliding surfaces, that is, the outboard portion of the outer peripheral surface of the inner member 32 and the seal contact member 45. Once this phenomenon occurs, respective contact pressures between the elastic sealing lips 40a and 42a and the associated sliding surfaces increase, which in turn result in increase of frictional resistance.
When it comes to automotive vehicles, a demand for realization of a high mileage is increasing and, for this reason, various attempts have hitherto been endorsed. For example, so far as the wheel support bearing assembly is concerned, weight saving of the bearing assembly itself and reduction in frictional resistance occurring in moving components are called for. One of major causes of the increased frictional resistance in the bearing assembly includes preload and seal torque, and the torque brought about by the contact seal discussed above largely affects the frictional resistance occurring in the wheel support bearing assembly.